Dynamic spatio-temporal contribution of single β5t+ cortical epithelial precursors to the thymus medulla

Intrathymic T‐cell development is critically dependent on cortical and medullary thymic epithelial cells (TECs). Both epithelial subsets originate during early thymus organogenesis from progenitor cells that express the thymoproteasome subunit β5t, a typical feature of cortical TECs. Using in vivo lineage fate mapping, we demonstrate in mice that β5t⁺ TEC progenitors give rise to the medullary TEC compartment early in life but significantly limit their contribution once the medulla has completely formed. Lineage‐tracing studies at single cell resolution demonstrate for young mice that the postnatal medulla is expanded from individual β5t⁺ cortical progenitors located at the cortico‐medullary junction. These results therefore not only define a developmental window during which the expansion of medulla is efficiently enabled by progenitors resident in the thymic cortex, but also reveal the spatio‐temporal dynamics that control the growth of the thymic medulla.

MAPK Phosphatase 5 Expression Induced by Influenza and Other RNA Virus Infection Negatively Regulates IRF3 Activation and Type I Interferon Response

The type I interferon system is essential for antiviral immune response and is a primary target of viral immune evasion strategies. Here, we show that virus infection induces the expression of MAPK phosphatase 5 (MKP5), a dual-specificity phosphatase (DUSP), in host cells. Mice deficient in MKP5 were resistant to H1N1 influenza infection, which is associated with increased IRF3 activation and type I interferon expression in comparison with WT mice. Increased type I interferon responses were also observed in MKP5-deficient cells and animals upon other RNA virus infection, including vesicular stomatitis virus and sendai virus. These observations were attributed to the ability of MKP5 to interact with and dephosphorylate IRF3. Our study reveals a critical function of a DUSP in negative regulation of IRF3 activity and demonstrates a mechanism by which influenza and other RNA viruses inhibit type I interferon response in the host through MKP5.